We will develop a novel detector modules for a new class of solid state gamma cameras, offering superior performance compared with currently available systems, which will be capable of excellent energy resolution, good sensitivity down to 27 keV for small animal imaging applications and also the ability to clearly separate closely spaced higher energy gamma-rays for dual-isotope imaging applications. This new gamma camera technology will be based on Photon Imaging's new silicon photodiodes and a new low noise multi-channel ASIC (application specific integrated circuit), recently developed by scientists at the Brookhaven National Laboratory (BNL). The BNL ASIC is particularly well suited for this application due to its low noise, charge sensitive preamplifier, and peaking time regime. In addition, other chip specifications are ideally matched to the silicon photodiode. Improvements in the overall noise system level, and the ability to fabricate large area arrays using the relatively inexpensive technology afforded by the silicon ASIC and silicon photodiodes, will result in robust gamma cameras with improved energy resolution and improved sensitivity. Improved energy resolution will lead directly to higher sensitivity, better contrast, improved spatial resolution and the capability to perform quantification of SPECT images. In Phase I, Photon Imaging will work closely with BNL staff to evaluate the existing ASIC performance in conjunction with new silicon photodiodes that Photon has been developing for coupling with CsI(TI) scintillator arrays. Several channels will be characterized in response to gamma radiation from radioisotope sources. Full energy spectra will be collected per channel. Modifications for the chip will be proposed for optimum performance in medical imaging applications. In Phase II, the chip will be modified to optimize the chip with respect to shaping time, analog outputs, gain and other parameters based on the Phase I evaluation. Phase II will include design, fabrication and characterization of the modified ASIC, and full fabrication of a prototype detector array comprised of a 16x16 array for 256-channels of readout. The prototype detector array will be evaluated with radioisotope sources and medical imaging phantoms.